We're just two weeks into the 2013 season, and yet we already have some closer controversies. In Kansas City, Greg Holland is under the microscope after giving up four runs in his first three innings of work, and in Milwaukee, John Axford is getting knocked around for the second straight year. The situations differ, however, because of the men who are in line to replace them.

For the Royals, 23-year-old flamethrower Kelvin Herrera is the reliever in waiting. Herrera threw 162 three-digit fastballs last season, more than any other pitcher in a season since 2002 other than Aroldis Chapman (also in 2012) and Joel Zumaya, who did it three different times in the previous decade. Herrera has the raw stuff that people tend to associate with elite closers, and so it is little surprise that at the first sign of problems for Holland, the Herrera-as-closer speculation has begun.

The Brewers, on the other hand, are looking to Jim Henderson, a career minor leaguer who made his major league debut in 2012 at age 30 and had limited success in his brief time in the role a season ago.

The difference in age (and pedigree) of the two pitchers got me wondering about how much a closer's age at debut is predictive of success. I ran the numbers, and the results give us a good sense of how successful Herrera and Henderson will (or won't) be.

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